Used lubricating and hydraulic oils are generated, for example, by automotive and commercial shops, large industrial manufacturing facilities, marine facilities and airline and railroad maintenance departments. Used oils are generally considered hazardous wastes and are heavily regulated. Generators of used oils are responsible for cradle to grave management (RICRA) of these waste streams. Generators have generally contracted with used oil recyclers to pick up the waste and remediate it or dispose of it under the laws that regulate the transport, processing and destruction of the various components that make up these particular waste streams. However, under current United States laws, having used oil picked up does not remove the potential liability from the generator. Moreover, such used oil can only be efficiently disposed of (e.g., through combustion) if it is treated to remove aqueous contamination.
There is no equipment available that can easily and cost-effectively remediate these waste streams on-site. The generators must contract with firms that have special expertise in reclaiming these waste streams as an on-site service. This service is costly. The predominant method of disposal of used oils is to contract with a used oil recycler. Depending on the characteristics of the oily waste stream and petroleum market conditions, the cost of this service varies. When crude oil prices were depressed (e.g., below $22 per barrel), used oil recyclers would pick up oily wastes that had less than 6% water (e.g., aqueous contamination) free of charge. If the waste had more than 6% water used oil recyclers would charge the generator a fee per volume obtained for disposal.
When used oil recyclers pick up oil from generators that had less than 6% water content, this oil is transported back to the used oil processing facility and put in a good oil storage tank to be sold as a substitute for # 2 burning fuel. When crude oil prices were depressed, used oil recyclers might sell this product for around $0.20 per gallon. With current volatile crude oil prices, the price for used oil can rise with the crude market. If the waste oil had more than 6% water content, it must be transported back to a plant for processing (removing water) before it can be resold as burning fuel and its price will be inverse to its water content. This process for removing water from used oils is complex, costly, time consuming and produces waste components that require further remediation (rag layer).
A typical process involves (for example at Aaron Oil, Mobile, Ala.) transferring used oils that come in on trucks from multiple generators to a used oil holding tank. Once the tank reaches a certain level, it is transferred to another process tank, where it is mixed to produce a consistent product. Once mixed, a sample is taken from the tank for process bench testing. Bench testing involves the heating of numerous samples and the addition of multiple demulsifer chemicals at various concentrations. After the samples are heated and dosed with demulsifiers, they are allowed to cool and visually inspected. This process can take up to two hours.
Visual inspection shows which demulsifier and at which concentration is most effective in breaking the water and solids out of the starting sample. The most successful demulsifier at minimal concentrations is picked for the actual production run. It should be noted that even with bench testing and a good result with a particular demulsifer, this does not always lead to a successful result during the production run, which requires the production batch to be processed again.
Once the optimal production demulsifier is chosen, the process tank, which often holds 60,000 liters, is heated by drawing off the bottom and running through a gas fired heater and put back into the top of the tank. This heating process goes on until the tank reaches about 60° C. (140° F.) and demulsifiers are added at the middle to the end of the heating process. The heating process takes between 8 to 12 hours to bring the 60,000 liter tank to temperature, at which point it is allowed to stand in a quiet condition for up to another 24 hours.
Near the end of the 24 hours, the tank is sampled to see how much water has been broken out from the starting used oil. Once it has been determined through sampling that the separation process has completed, the solids and water are drawn off and the water is treated in the waste-water treatment plant and solids go to disposal.
Above the water in the process tank is a rag layer (Off-Spec Oil). This layer contains mostly water but with high oil content and some solids. This waste stream must be disposed of at additional cost. Above the rag layer lies the good oil (On-Spec Oil) with less than 6% water content that is transferred to a good oil holding tank for resale as a substitute for #2 burning fuel. This batch process is complex (not fool proof), lengthy, and somewhat labor intensive. It is also costly having rising natural gas costs for heating and demulsifier costs.
Other techniques for treating used oil above 6% water have included, for example, gravitational settling that results in waste products consisting of a stable oil/water emulsion mixed with solid minerals. The emulsion material constitutes unusable waste that is stored in open pits or temporary holding tanks. Increasing regulatory and environmental pressure, and liabilities are forcing owners of these waste product impoundments to clean up these sites and safely dispose of the waste.
Other techniques for waste oil emulsion remediation include the use of gas-fired heaters, microwave heaters, microbes, centrifuges, and chemicals. However, these methods do not recover a fully marketable product. They provide only partial separation and typically leave large amounts of regulated waste. Those methods that do recover some marketable oil are inefficient, making satisfactory results difficult to obtain. Specifically, conventional heating methods suffer from slow heat transfer between the heating element and thick emulsions, accumulation of heavy layers of solid residue on heat transfer surfaces, and loss of volatiles. Chemical demulsifiers, such as alum and polyamines, can be used to separate oil/water emulsions, but these chemicals are subject to very strict government regulation concerning their discharge into public water. In addition, chemical treatment can be a relatively slow process with an inefficient separation of some emulsions.
Thus, there exists a need for an apparatus and process of treating waste oil above 6% water that recovers marketable oil efficiently and more economically. The present invention was made to address this need.